Variable-force coil spring and pulling cord control device

Abstract

A variable-force coil spring includes a central hole and a band coiled from the central hole outward. The band includes an inner end located in the central hole, an outer end, and an outer end section from the outer end to a first length, a first force descending section generating gradually descending elastically restoring force from the first length to a second length, a second force descending section generating gradually descending elastically restoring force from the second length to a third length, and a force maintaining section generating maintained elastically restoring force from the third length to a fourth length, which are successively arranged from the outer end toward the inner end in order. The present invention further provides a pulling cord control device including a variable-force coil spring. The present invention is applicable to a window blind to make it convenient and easy to be upward folded smoothly.

What is claimed is: 
     
         1 . A variable-force coil spring comprising a central hole and a band coiled from the central hole outward, the band comprising an inner end located in the central hole, an outer end, and a plurality of sections arranged from the outer end toward the inner end successively, the plurality of sections, from the outer end toward the inner end in order, comprising:
 an outer end section from the outer end to a first length;   a first force descending section generating gradually descending elastically restoring force from the first length to a second length;   a second force descending section generating gradually descending elastically restoring force from the second length to a third length; and   a force maintaining section generating maintained elastically restoring force from the third length to a fourth length.   
     
     
         2 . The variable-force coil spring as claimed in  claim 1 , wherein the force maintaining section generates consistent elastically restoring force from the third length to the fourth length. 
     
     
         3 . The variable-force coil spring as claimed in  claim 1 , wherein the force maintaining section generates gradually ascending elastically restoring force from the third length to the fourth length, and an ascending rate of the elastically restoring force of the force maintaining section is smaller than a descending rate of the elastically restoring force of the first force descending section and smaller than a descending rate of the elastically restoring force of the second force descending section. 
     
     
         4 . The variable-force coil spring as claimed in  claim 1 , wherein a descending rate of the elastically restoring force of the first force descending section is larger than a descending rate of the elastically restoring force of the second force descending section. 
     
     
         5 . The variable-force coil spring as claimed in  claim 1 , wherein a descending rate of the elastically restoring force of the first force descending section is smaller than a descending rate of the elastically restoring force of the second force descending section. 
     
     
         6 . The variable-force coil spring as claimed in  claim 5 , wherein the elastically restoring force of the first force descending section non-linearly descends from the first length to the second length first quickly and then slowly. 
     
     
         7 . A pulling cord control device comprising:
 a housing;   at least one cord winding wheel and a coil spring winding wheel, which are disposed in the housing capably of rotating each other; and   a variable-force coil spring comprising a central hole and a band coiled from the central hole outward, the band comprising an inner end located in the central hole, an outer end, and a plurality of sections arranged from the outer end toward the inner end successively, the variable-force coil spring being arranged to be affected by an external force to be wound onto the coil spring winding wheel from an initial installed status, when the variable-force coil spring is in the initial installed status, the outer end of the band being disposed on the coil spring winding wheel, the sections of the band wound onto the coil spring winding wheel from the initial installed status in order comprising:   a first force descending section generating gradually descending elastically restoring force from a first length to a second length;   a second force descending section generating gradually descending elastically restoring force from the second length to a third length; and   a force maintaining section generating maintained elastically restoring force from the third length to a fourth length.   
     
     
         8 . The pulling cord control device as claimed in  claim 7 , wherein the pulling cord control device further comprises a coil spring sleeving wheel; the at least one cord winding wheel, the coil spring winding wheel and the coil spring sleeving wheel are disposed in the housing capably of rotating each other; the variable-force coil spring is sleeved onto the coil spring sleeving wheel. 
     
     
         9 . The pulling cord control device as claimed in  claim 7 , wherein the force maintaining section of the variable-force coil spring generates consistent elastically restoring force from the third length to the fourth length. 
     
     
         10 . The pulling cord control device as claimed in  claim 7 , wherein the force maintaining section of the variable-force coil spring generates gradually ascending elastically restoring force from the third length to the fourth length, and an ascending rate of the elastically restoring force of the force maintaining section is smaller than a descending rate of the elastically restoring force of the first force descending section and smaller than a descending rate of the elastically restoring force of the second force descending section. 
     
     
         11 . The pulling cord control device as claimed in  claim 7 , wherein a descending rate of the elastically restoring force of the first force descending section of the variable-force coil spring is larger than a descending rate of the elastically restoring force of the second force descending section. 
     
     
         12 . The pulling cord control device as claimed in  claim 7 , wherein a descending rate of the elastically restoring force of the first force descending section of the variable-force coil spring is smaller than a descending rate of the elastically restoring force of the second force descending section. 
     
     
         13 . The pulling cord control device as claimed in  claim 12 , wherein the elastically restoring force of the first force descending section of the variable-force coil spring non-linearly descends from the first length to the second length first quickly and then slowly.